Phosphor screen

Abstract

This invention relates to phosphor screens for converting X-rays into visible or near visible radiation. The screens comprise in a fluorescent layer a phosphor mixture which consists of a fluorohalide corresponding to the formula [Ba(1-x-y-p) SrxCayEup] F [Cl(1-a-b)BraIb](1) WHEREIN Y </= 0.

What we claim is: 
     
       1. An X-ray intensifying screen which comprises in a fluorescent layer a phosphor mixture which consists of an alkaline earth fluorohalide activated with divalent europium having the empirical formula   [Ba.sub.(l.sub.-x.sub.-y.sub.-p) Sr.sub.x Ca.sub.y Eu.sub.p ] F [Cl.sub.(l.sub.-a.sub.-b) Br.sub.a I.sub.b ]     where   y ≦ 0.20   x + y + p ≦  l   a + b ≦  l   0.001 ≦ p ≦ 0.20 together with at least one phosphor which is either calcium tungstate or which is a rare earth oxychalcogenide having the formula     [M.sub.(l.sub.-x) A.sub.x ].sub.2 O.sub.2 Ch     wherein M is at least one rare earth host element, A is an activator which is a rare earth element different from M and which has an atomic number from 59 to 71, Ch is sulphur, selenium or tellurium and 0.001 ≦ x ≦ 0.2.     
     
     
       2. An X-ray intensifying screen according to claim 1 wherein y in the formula of the alkaline earth fluorohalide is 0. 
     
     
       3. An X-ray intensifying screen according to claim 1 which comprises in a fluorescent layer a phosphor mixture which consists of a barium fluorohalide activated with divalent europium having the formula   Ba.sub.(l.sub.-p.sbsb.1) FCl(Eu.sub.p.sbsb.1)     where   0.001 ≦P l  ≦ 0.20 together with at least one phosphor which is either calcium tungstate or which is a rare earth oxychalcogenide having the formula     [M.sub.(l.sub.-x) A.sub.x ].sub.2 O.sub.2 Ch     wherein M is at least one rare earth host element, A is an activator which is a rare earth element different from M and which has an atomic number from 59 to 71, Ch is sulphur, selenium or tellurium and 0.001 ≦ x ≦ 0.2.     
     
     
       4. An X-ray intensifying screen according to claim 3 where 0.02 ≦ p ≦ 0.05. 
     
     
       5. An X-ray intensifying screen according to claim 1 wherein M is lanthanum, gadolinium, yttrium or lutetium. 
     
     
       6. An X-ray intensifying screen according to claim 1 where in the formula of the rare earth oxychalogenide as defined in claim 1 A represents praeseodymium, europium, dyprosium, ytterbium, terbium, samarium or thulium. 
     
     
       7. An X-ray intensifying screen according to claim 1 where in the formula of the rare earth oxychalogenide as defined in claim 1 Ch represents sulphur. 
     
     
       8. An X-ray intensifying screen according to claim 1 which comprises a phosphor mixture which consists of barium fluorchloride containing a small amount of europium as activator and which has the formula   BaFCL(Eu)     together with either gadolinium oxysulphide containing a small amount of terbium as activator and which has the formula     Gd.sub.2 O.sub.2 S(Tb)     or yttrium oxysulphide containing a small amount of terbium as activator and which has the formula     Y.sub.2 O.sub.2 S(Tb).     
     
     
       9. An X-ray intensifying screen according to claim 1 which comprises a dimensionally stable support base there being present thereon in order a light reflecting layer (optional), a fluorescent layer which comprises in a binder a phosphor mixture as defined in claim 1 and a protective layer. 
     
     
       10. An X-ray intensifying screen according to claim 9 wherein the coating weight of the mixed phosphors in the fluorescent layer is from 2- 20 g/dm 2 .